An image sensor may be a semiconductor device to convert an optical image into an electrical signal. The image sensor may be generally classified into a charge coupled device (CCD) and a CMOS image sensor (CIS).
The CCD may have a complicated driving method and high power consumption. It may also require a plurality of photolithography processes during fabrication. Accordingly, the CCD may have a disadvantage of having complicated manufacturing process. CMOS image sensors may be considered as next generation image sensors and may overcome various disadvantages of the CCD.
The CMOS image sensor may include photodiodes and MOS transistors in a unit pixel, and may sequentially detect electrical signals of respective unit pixels in a switching manner to realize an image.
FIG. 1 is an example cross-sectional diagram of a related art CMOS image sensor.
Referring to FIG. 1, interlayer insulating layer 108 may be formed on a substrate (not shown), which may include transistors (not shown) and photodiodes (not shown). A variety of metal lines 109 may be formed with a substantially constant interval on interlayer insulating layer 108.
First overcoat layer 110 may be formed on a surface (for example, the entire surface) of semiconductor substrate including metal line 109. Color filter layer 111 may be formed on first overcoat layer 110.
Also, second overcoat layer 112 may be formed on a surface (for example, the entire surface) of semiconductor substrate including color filter layer 111. Microlenses 113 may be formed on second overcoat layer 112 to correspond to locations of respective color filters of color filter layer 111.
Hemisphere-shaped microlenses 113 may be formed, for example by coating a resist on second overcoat layer 112, selectively patterning the resist to form a resist pattern, and performing reflow on the resist pattern at a prescribed temperature.
However, according to the related art, the hemisphere-shaped microlenses may be formed by forming a resist pattern on second overcoat layer 112 and performing reflow on the resist pattern. Therefore, a degree of light condensing may be low.
Also, according to the related art, a lens shape may be difficult to control. Therefore, controlling an aspherical coefficient may not be easy.
Also, according to the related art, adjacent microlenses may merge together depending on density of the resist pattern.